Ticket #41998: 41998.patch

src/wp-includes/default-constants.php

@@ -92 +92 @@
                 define( 'SCRIPT_DEBUG', $develop_src );
         }
 
+        // Add define( 'WP_DEBUG_REST_API', true ); to wp-config.php to enable pretty JSON in the REST API during development.
+        if ( ! defined( 'WP_DEBUG_REST_API' ) )
+                define( 'WP_DEBUG_REST_API', false );
+
         /**
          * Private
          */

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -393 +393 @@
                          */
                         $result = apply_filters( 'rest_pre_echo_response', $result, $this, $request );
 
-                        $result = wp_json_encode( $result );
+                        $options = ( defined( 'WP_DEBUG_REST_API' ) && WP_DEBUG_REST_API ) ? JSON_PRETTY_PRINT : 0;
+
+                        $result = wp_json_encode( $result, $options );
 
                         $json_error_message = $this->get_json_last_error();
                         if ( $json_error_message ) {